Treatment of drinking water to remove PFAS (Signal)

Occurrence of PFAS in drinking water 

Per- and polyfluoroalkyl substances (PFAS) is the name given to a group of around 10,000 synthetic compounds that have been used extensively for many decades in e.g. non-stick pots and pans, food packaging, cleaning products, textiles and industrial processes, because of their unique chemical and physical properties. Numerous PFAS are associated with adverse health effects in humans (including liver damage, thyroid disease, obesity, fertility issues and cancer). They are highly persistent and/or mobile in the environment and can bioaccumulate in wildlife and humans. PFAS are now found everywhere in the environment. They contaminate surface- and groundwater, including drinking water; in the EU, 65% of the drinking water is derived from groundwater. 

Le Monde recently published the Map shown above; it provides the most up-to-date information on the extent and levels of PFAS contamination in soil, groundwater and surface water across Europe. Sites where contamination has been detected between 2003 and 2023 are presented on the map along with PFAS manufacturing facilities, sites where PFAS are used, and sites that are likely to be contaminated due to current or past industrial activity. However, there are still not sufficient data in Europe to fully understand the extent to which these parts of the environment are contaminated with PFAS. Additionally, further data are required to understand PFAS contamination in other areas such as drinking water, sewage sludge and air.

People are most commonly exposed to PFAS through contaminated food and drinking water and such contamination has been reported in many parts of Europe. The recast Drinking Water Directive (DWD) (EU) 2020/2184 limits total PFAS in drinking water to 0.5 µg/l. It also states that the levels of 20 individual PFAS must each be below 0.1 µg/L. Member States will be required to comply with these levels from 2026. In practice this means that drinking water will need to be assessed going forward to ensure compliance with the Directive. Where levels of PFAS exceed the limits, measures can be taken to remove them from drinking water. Results reported from monitoring under the DWD will also help PFAS pollution be tracked. 

Treatment possibilities 

Once PFAS have entered the environment, it is very challenging to remove them. It is hard to measure PFAS in drinking water as they include a large number of individual compounds with typically low concentrations. The recast DWD requires the European Commission to establish technical guidelines for analytical methods for monitoring PFAS by 2024. These guidelines must include information on detection limits, maximum concentration levels and sampling frequency. Conventional drinking water treatment processes, such as coagulation, flocculation, air stripping, ozonation, chlorination or rapid sand filtration, are ineffective in removing PFAS from water.

One possible solution to achieve low enough concentrations of pollutants is to dilute drinking water with water from other sources. Some more novel technologies also exist and are currently being developed. For example, the United States Environmental Protection Agency (USEPA) Drinking Water Treatability Database gives an overview of effective technologies for reducing PFAS in drinking water and includes activated carbon adsorption, ion exchange resins and high-pressure membranes, such as nanofiltration or reverse osmosis.

Specific case studies from European countries using these technologies are available. For example, a significant case of PFAS contamination of drinking water was discovered in 2013 in the Veneto Region, Italy, primarily due to industrial emissions from a nearby PFAS manufacturer. In this case, granular activated carbon (GAC) adsorption was used effectively to remove PFAS during drinking water treatment.  

While the potential of various technologies has been widely demonstrated in the laboratory or in pilot projects, they have not yet been proven to remove the full range of PFAS in drinking water when used more broadly. Additionally, there are a number of technical and economic challenges. For example, the effectiveness of the techniques varies depending on where they are being used. Other circumstances and certain environmental factors (e.g. the presence of organic matter) which cannot be controlled can make them less effective. Additionally, certain techniques are more effective for some types of PFAS compared to others. Some are shown to be highly effective for long-chain PFAS but less so for short-chain PFAS. These techniques also involve significant capital and operational costs (e.g. due to high energy requirements). For example, from 2013–2018, Acque del Chiampo S.p.A. invested about EUR 2.3 million in the installation of activated carbon filters, water supply networks and laboratory equipment; additionally, an investment programme of about EUR 21 million up to 2023 was planned to remediate the most contaminated sites. 

Furthermore, these techniques capture PFAS rather than destroy them. Consequently, residual waste streams are generated. These can be difficult and costly to treat or dispose of, as they may have to be sent for incineration or to landfills. More advanced methods to capture and permanently destroy PFAS for drinking water are being investigated. For example, a solution to break down PFAS is being investigated by Aarhus University, Denmark, but it is still a long way from being operationalised.